一、虚拟语气用于定语从句中在It is (high, about)time(that)…句型中，that引导的定语从句中的谓语常用一般过去时来构成虚拟语气。例：It’s about time that we put an end to this controversy.现在该是我们停止这场争论的时候了。例：It is time we went to bed.我们该去睡觉了。二、虚拟语气用于if only 引导的从句中在if only引导的从句中，谓语动词须采用虚拟语气，其用法与wish后宾语从句的用法基本相同，表示“但愿”，“要是…就好了”的意思。例：If only I knew what you wanted.要是我知道你需要什么就好了。例：If only he had arrived in time,he would not have been punished.他要是准时到达就好了。经典练习：1、It’s already six o’clock now. Don’t you think it’s about time____?A)we are going homeB)we go homeC)we went homeD)we can go home2、If only the committee____the regulations and put them into effect as soon as possible.A)approveB)will approveC)can approveD)would approve3、It’s necessary____the dictionary immediately.A)that he will returnB)that he returnedC)that he returnD)that he has to return4、She must have had an accident, or he____then.A)would have been hereB)had to be hereC)should be hereD)would be here5、I apologize if I ____you, but I assure you it was unintentional.A)offendedB)had offendedC)should have offendedD)might have offended解析：1、答案选C)。在it’s about time that…..句型中，定语从句的谓语动词应用过去时来表示虚拟语气。所以C项是正确的。2、答案选D)。if only表示一种愿望，谓语用“would+动词原形”表示对将来事实的愿望，所以D是正确的。3、答案选C)。在由it is necessary 等引导的主语从句要使用虚拟语气，虚拟语气的谓语动词用“should+动词原形”或动词原形。4、答案选A)。由or引出的是与事实相反的假设条件，因此空缺处应填入表示虚拟语气的谓语动词。前一个分句中表示的是过去的时间，所以后一分句要用would have done的形式。所以A是正确的。5、答案选B)。本题中but分句中的it was 表明事情发生在过去，因此条件句应用过去完成时，表示与过去事实相反，所以B是正确的。